Apparatus and process for stacking sheets of half-cell structure to make a honeycomb core

ABSTRACT

The present invention relates to an apparatus and a process for a half-cell structure to make a hexagonal-cell honeycomb core. The structure has a plurality of peaks and valleys and a diagonal surface between each consecutive peak and valley. The apparatus comprises a stack holder for stacking the structure so that as one sheet is placed on top of a stack comprising at least one sheet, the peaks of one sheet contact the peaks of an adjacent sheet. The apparatus also comprises an air blower disposed beneath the top of the stack for reducing the air pressure surrounding the stack to a pressure below the air pressure on the top of the stack, thereby pressing the layers together to form the core.

FIELD OF THE INVENTION

The present invention relates to an apparatus and a process for stackinga half-cell structure to make a hexagonal-cell honeycomb core and atransfer head and a process for holding the half-cell structure.

DESCRIPTION OF THE RELATED ART

Devices for stacking a corrugated medium are known. For example, U.S.Pat. No. 3,044,921 to Wentworth et al. discloses a system of stackingcorrugated aluminum foil by providing mating projections along the foiland partial cuts across the foil at the top of a corrugation to createhinge lines. The projections of one layer register with the corrugationsof an adjacent layer. The foil is coated on the tops and bottoms of thecorrugations with adhesive and manually folded back and forth to form acore on a movable platform. Alternatively, adhesive is applied and driedon the tops and bottoms of the corrugations, and projections are punchedin the tops and bottoms. The foil is then cut into uniform length sheetswhich are stacked by hand on a movable platform. In either case, thecore, after stacking, is placed under heat and pressure to bond thelayers or the sheets, respectively, at the adhesive-coated contactareas.

U.S. Pat. No. 2,518,164 to Meyer discloses a system for assemblingsheets of half-cell structure to form a core where a sheet coated with athermoset adhesive is manually placed on a heated work holding plate. Asheet pick-up plate carries at its opposite longitudinal edges two rowsof sheet pick-up pins. When the sheet pick-up plate holding previouslyassembled sheets is lowered onto the work holding plate, the pins aredriven through the edge of the heated sheet. The work holding plate isheated to cure the adhesive on the sheet placed there. When the core iscompleted, it is removed from the pins. Alternatively, the core may beremoved from the pins and placed in an oven to allow the adhesive tocure. In another embodiment, tubular binding elements penetratesuccessive sheets and aid in the preservation of the condition of thecore in which it was assembled and in the removal of the core from thepins.

U.S. Pat. No. 3,887,418 to Jurisich discloses an apparatus and a processfor forming a honeycomb core where two webs are corrugated to formcrests and troughs. Adhesive is applied to the crests and troughs of oneof the webs, and the other web is left uncoated. Layers of the web arethen stacked so that the crests and troughs nest one inside of anotherand so as to alternate an adhesive coated corrugated web with anuncoated corrugated web. Heat and/or pressure is then applied to thestack to effect bonding of the stacked web. Heated continuous belts gripthe sides of the bonded stacked to heat it for curing and pull it apartto expand the stack and form the open honeycomb structure.

The configurations for stacking in such known devices are complicated,time-consuming and thus expensive. Moreover, registration of the sheetswith pins and projections produces waste product that often must beremoved after assembly.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anapparatus and a process for stacking sheets of half-cell structure whichaccurately align the sheets without waste as they are stacked to form ahoneycomb core.

It is also an object of the present invention to provide an apparatusand a process for stacking sheets that are simple and thus economical.

A further object of the present invention is to provide an apparatus anda process for stacking sheets which produce a honeycomb core which isaccurate and inexpensive to manufacture.

Another object of the present invention is to provide a transfer headand a process for holding a half-cell structure.

In order to achieve the foregoing objects, there is provided anapparatus for stacking a half-cell structure to make a hexagonal-cellhoneycomb core. The structure has a plurality of peaks, a plurality ofvalleys and a diagonal surface between each consecutive peak and valley.The apparatus comprises a stacking mechanism for stacking the layers sothat as one layer is placed on the top of a stack comprising at leastone layer, the peaks of one layer contact the peaks of an adjacentlayer. The apparatus also comprises a differential pressure mechanismdisposed beneath the top of the stack for reducing the air pressuresurrounding the stack to a pressure below the air pressure on the top ofthe stack, thereby pressing the sheets together to form the core.

Further in accordance with the present invention, there is provided atransfer head for holding at least one sheet of half-cell structure. Thetransfer head comprises a plurality of support bars for supporting thesheet and at least one space formed between each support bar. The widthof each space is about the distance between adjacent valleys of thehalf-cell structure, and the depth of the space is greater than theheight of the peaks.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and a part of thisspecification, illustrate various embodiments of the and together withthe description, serve to explain the principles invention.

FIG. 1 is an overall, perspective view of a system for forming ahoneycomb half-cell structure from a supply of material and forproducing a honeycomb core from the half-cell structure according to thepresent invention.

FIG. 2 is an exploded view of a corner section of the assembledhoneycomb core of the present invention.

FIG. 3 is a schematic view of a portion of a half-cell forming apparatusof the present invention.

FIG. 4 is an enlarged, schematic view of the bars and the back-up platesof the half-cell forming apparatus of the present invention.

FIG. 5A is an end view of a portion of a half-cell forming apparatustaken across lines 5A--5A of FIG. 5B.

FIG. 5B is a side view of the half-cell forming apparatus as shown inFIG. 1.

FIG. 6 is an enlarged perspective view of an adhesive-coated half-cellstructure.

FIG. 7A is a side view illustrating the application of first and secondadhesive components to the peaks of a half-cell structure according toan alternative embodiment of the present invention.

FIG. 7B is a side view illustrating stacking the half-cell structureaccording to the alternative embodiment of the present invention shownin FIG. 7A.

FIG. 8A is a side view illustrating the application of first and secondadhesive components to the peaks of a half-cell structure according toanother alternative embodiment of the present invention.

FIG. 8B is a side view illustrating folding the half-cell structureaccording to the other alternative embodiment of the present inventionshown in FIG. 8A.

FIG. 9A is an enlarged perspective view of an adhesive applyingapparatus of the present invention as shown in FIG. 1.

FIG. 9B is an enlarged portion of the half-cell structure in contactwith a back-up roll and a gravure roll of the adhesive applyingapparatus as shown in FIG. 9A.

FIG. 10A is an enlarged plan view of a portion of a cutting apparatus ofthe present invention as shown in FIG. 1.

FIG. 10B is a cross-sectional view of the cutting apparatus taken acrosslines 10B--10B of FIG. 10A showing a plurality of conveyor platens and astacker arm in position for picking up a sheet of half-cell structure.

FIG. 10C is a shifted view of the cross-sectional view of FIG. 10B andshowing different platens in position for cutting the half-cellstructure than those shown in FIG. 10B.

FIG. 11 is a partial plan view taken across lines 11--11 of FIG. 12showing the conveyor and conveyor positioning sensors for locating thehalf-cell structure at a blade of the cutting apparatus of the presentinvention.

FIG. 12 is a cross-sectional view of the channel of the conveyor takenacross lines 12--12 of FIG. 13.

FIG. 13 is a cross-sectional view of the conveyor taken across lines13--13 of FIG. 11.

FIG. 14A is a cross-sectional view of a stacking apparatus of thepresent invention taken across lines 14A--14A of FIG. 1.

FIG. 14B is a partial cross-sectional view taken across lines 14B--14Bof FIG. 14A showing the end guide plates for the core in a stack holderof the stacking apparatus.

FIG. 15 is an enlarged cross-sectional view of the stack holder of FIG.14A showing the differential pressure zones of the air in the stackholder.

FIG. 16 is a partial cross-sectional view of an alternate embodiment ofthe stack holder that uses a heated transfer head on the stacker arm.

FIG. 17 is a timing diagram which illustrates the control system logicfor operating the system for producing a honeycomb core from thehalf-cell structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Whenever possible, the same reference numberswill be used throughout the drawings to refer to the same parts.

FIG. 1 is an overall perspective view of a system, shown generally at10, for forming a honeycomb half-cell structure from a supply ofmaterial and for producing a hexagonal-cell honeycomb core from thehalf-cell structure. The individual apparatus of system 10 may beoperated in a stand-alone, batch process or in an integrated, over-allprocess.

In accordance with the present invention, there is provided a half-cellforming apparatus for making a honeycomb half-cell structure from acontinuous web of material. A half-cell forming apparatus is shown at 20in FIG. 1 which forms a continuous supply of honeycomb half-cellstructure from the material. Apparatus 20 is part of over-all system 10and will be described in greater detail below. As shown in FIG. 1,apparatus 20 comprises a continuous web unwind stand, shown generally at21 in FIG. 1, for storing a supply of the material. Web unwind stand 21includes a spool 22, a disc 22a, a tensioning roll assembly 22b, and aconventional brake mechanism (not shown). The brake mechanism engagesdisc 22a to resist unwinding of spool 22 by tensioning roll assembly22b. Thus, the brake mechanism, disc 22a and roll assembly 22bmaintaintension on the unwinding web as it is drawn through half-cell formingapparatus 20. A formed half-cell structure is shown at 23 in FIG. 1exiting half-cell forming apparatus 20.

In accordance with the present invention, there is provided an apparatusfor applying at least one adhesive component to the honeycomb half-cellstructure. The apparatus for applying the adhesive component is shown at24 in FIG. 1. Apparatus 24 is part of over-all system 10, and will bedescribed in greater detail below. An adhesive-coated half-cellstructure is shown exiting the adhesive applying apparatus at 25 in FIG.1.

In accordance with the present invention, there is provided an apparatusfor cutting the continuous supply of honeycomb half-cell structure intoa plurality of sheets. The cutting apparatus of the present invention isshown generally at 26 in FIG. 1. Cutting apparatus 26 is a part ofoverall system 10, and will be described in greater detail below.

In accordance with the present invention, there is provided an apparatusfor stacking a plurality of sheets of half-cell structure to make ahexagonal-cell honeycomb core. The apparatus is shown at 29 in FIG. 1.Apparatus 29 is part of over-all system 10, and will also be describedbelow in greater detail. Apparatus 29 includes a stacker arm 31 fortransferring the sheets to the top of a stack of sheets of half-cellstructure and a stack holder 32 for supporting the stack of sheets.Stacking apparatus 29 also includes an air handling system 33 forproviding conditioned air for heating the stack of sheets in the stackholder to cure an adhesive system applied thereto and a heated enclosure34. The sheets are pressed together while they are heated, therebyforming a hexagonal-cell honeycomb core 30. Core 30 is shown sitting instack holder 32 in FIG. 1.

FIG. 2 is an exploded view of a corner section of the assembledhoneycomb core, where the assembled sheets are shown spaced apartslightly for the purpose of defining the half-cell structure surfacesand how they come together to make up the core. As shown in FIG. 2, eachsheet of half-cell structure in the assembled core, such as sheet 39,comprises a plurality of convex surfaces, or peaks, 42 on one side ofthe sheet and a plurality of concave surfaces, or valleys, 44 on thesame one side of the sheet. The other side of sheet 39 also comprises aplurality of convex surfaces, or peaks, 42' on the other side of thesheet and a plurality of concave surfaces, or valleys, 44', on the sameother side of the sheet. For reference purposes in FIG. 2, the one sideof the sheet of half-cell structure is facing up and the other side ofthe same sheet is facing down. Peaks 42 on the one side are oppositevalleys 44' on the other side, and valleys 44 on the one side areopposite peaks 42' on the other side. A diagonal surface 46 is formedbetween each consecutive peak and valley on the one side of the sheet,and a diagonal surface 46' is formed between each consecutive peak andvalley on the other side of the sheet. When a first sheet 39 ofhalf-cell structure is stacked on top of a second sheet 41 of half-cellstructure to form a core 30, peaks 42' on the other side of the firstsheet contact peaks 42" on the one top side of the second sheet.

Referring again to FIG. 1, system 10 also includes a central controlsystem 35 and distributed control centers 36, 37 and 38 which coordinatethe handling of the web of material or half-cell structure andtemperature monitoring and motion control in half-cell forming apparatus20, in adhesive applying apparatus 24 and in stacking apparatus 29,respectively. Various safety interlocks and emergency shut-downprocedures are monitored and implemented by central control system 35and by a plurality of distributed control systems 36, 37 and 38.Distributed control system 36 controls the speed and various methods ofheating the half-cell forming apparatus. It also provides processtemperature tension and speed monitoring for this apparatus. Distributedcontrol system 37 controls roll speed and resin temperature in adhesiveapplying apparatus 24. Distributed control system 38 controls theoperation of cutting apparatus 26, including the motion of conveyor 28,and the operation of stacking apparatus 29, including the motion ofstacker arm 31 and stack holder 32. It also controls the temperature inthe stack holder.

FIG. 3 is a schematic view of a portion of half-cell forming apparatus20 during the thermal cycle of the apparatus when the material of theweb is deformed and set. The half-cell forming apparatus of the presentinvention comprises means for positioning a length of the web whilemaintaining the tension thereof. The positioning means includes an upperloop 102 and a lower loop 104 as shown in FIG. 3. Upper loop 102comprises a plurality of upper bars 60a and 60b attached to a pair ofchains, and lower loop 104 comprises a plurality of lower bars 62a and62b, attached to another pair of chains. The bars of each loop includeat least one surface for contacting the web. Upper loop 102 and lowerloop 104 are disposed in a housing 128. A web 98 enters housing 128 atthe left in FIGS. 1 and 3 and is carried between the bars of the upperand lower loops as they travel in parallel alignment between an entrynip 106 and an exit nip 108. The web exits as formed half-cell structure23.

The half-cell structure in forming apparatus 20 is shown moreparticularly in FIG. 4. The web of material is placed between meshedbars 60a, 62a and bends back and forth over the corners, such as thoseshown at 68 and 70 in FIG. 4, of the bars. The width of the upper andlower bars, as illustrated by reference numerals 67 and 69,respectively, determines the width of the peaks and valleys of thehalf-cell structure. The creased form of the half-cell structure islocked in when it exits the half-cell forming apparatus at exit nip 108as shown in FIG. 3, so that the pitch of the half-cell structure issimilar to the pitch of the half-cell forming apparatus. The bars of thehalf-cell forming apparatus of the present invention are not to bedegraded by the high temperatures achieved during the operation of theapparatus. Also, the bars have a surface finish that does not stick tothe web. A bar material that has been found to work well with a varietyof webs is a nickel-coated carbon steel.

As shown in FIGS. 5A and 5B, the bars are connected to each other andsupported on each end by a pair of upper roller chains 70a and 70b and apair of lower roller chains 72a and 72b. Upper roller chains 70a and 70bare supported by a plurality of driven sprockets 74a and 74b disposed ona shaft 76 and a plurality of upper idler sprockets 78a and 78b disposedon an upper entrance shaft 80. Lower roller chains 72a and 72b aresupported by a plurality of driven sprockets 82a and 82b disposed on ashaft 84 and by a plurality of lower idler sprockets 86a, 86b disposedon a lower entrance shaft 88. Driven sprockets 74a and 82a and idlersprockets 78a and 86a are also shown in FIG. 3. Upper idler sprockets78a, 78b and lower idler sprockets 86a, 86b are all surrounded by anenclosure 110, although in FIG. 3 only idler sprockets 78a and 86a areshown surrounded by the enclosure. Shafts 76 and 84 are driven byengagement with a driving chain 90 as shown in FIG. 5B that is entrainedover an upper sprocket 92, a lower sprocket 94 and a motor-drivensprocket 96. Upper and lower sprockets 92 and 94, respectively, upperchains 70a and 70b and lower chains 72a and 72b, and upper bars 60a, 60band lower bars 62a, 62b must be carefully aligned by measuring the barlocations around shafts 76 and 84 for accurate positioning of the barsto make accurately formed half-cell structure. Upper idler sprockets78a, 78b and lower idler sprockets 86a, 86b are made as small aspractical to bring the attached bars into mesh over a small, sharpradius so the web is engaged between cooperating bars before it contactsand is restrained by succeeding bars.

The half-cell forming apparatus of the present invention comprises meansfor pre-heating the positioning means to at least the deformationtemperature of the web before the positioning means is placed in contactwith the web. Preferably, the pre-heating means comprises an inductioncoil 112 disposed adjacent the web-contacting surface of the bars ofupper loop 102 for heating upper bars 60a, 60b to a temperature abovethe web deformation temperature just before they enter enclosure 110.The pre-heating means also preferably includes an induction coil 118disposed adjacent the web-contacting surface of the bars of lower loop104 for heating lower bars 62a, 62b. Upper roller chains 70a, 70b, whichsupport bars 60a, 60b and lower roller chains 72a, 72b, which supportbars 62a, 62b, remain outside coils 112, 118, respectively, and are notheated by the coils. Preferably, induction coils 112, 118 heat theentire web-contacting surface of the bars of each loop. The pre-heatingmeans may also comprise any heating source, including, but not limitedto, a radiant heater, a convection heater, or an electrical resistanceheater. Upper bars 60a, 60b are supported relative to coil 112 by aslide 116, and lower bars 62a, 62b are supported relative to coil 118 bya slide 122. The pre-heating means also includes a plurality of forcedair blowers 103, 105 as shown in FIG. 3 disposed on the outer surface ofeach loop, which maintain the web deformation temperature on the barsestablished by induction coils 112 and 118.

The half-cell forming apparatus of the present invention also comprisesmeans for maintaining the tension on the positioning means and forcooling the positioning means to the stabilization temperature of theweb while holding the web thereon. The tension maintaining and coolingmeans comprises an upper back-up plate 124 and a lower back-up plate 126as shown in FIGS. 3 and 5B disposed on the respective inner surfaces ofthe bars of upper and lower loops 102, 104, respectively. In addition, aplurality of blowers 121 and 123 as shown in FIG. 3 is provided whichcirculate cooling air through the back-up plates and around bars 60a,60b and 62a, 62b and web 98. As shown in FIGS. 3 and 4, web 98 extendsbetween upper back-up plate 124 and lower back-up plate 126. It isimportant to ensure that the web is held tightly against the corners ofthe bars during cooling, thereby maintaining tension in the web, so thatsharp, accurate bends will be made in the web to form the half-cellstructure. Back-up plates 124, 126, in addition to cooling the bars,maintain the tension on the web.

As shown in FIGS. 5A and 5B, upper back-up plate 124 is pivotably heldat the upstream end on a plurality of threaded rods 404a, 404b by a nut418 on each rod and by a plurality of springs 420a, 420b held under aplate 422. Springs 420a and 420b do not permit vertical translation ofback-up plate 124 along rods 404a and 404b, respectively, but they dopermit rocking and thereby acts as a pivot for one end of upper back-upplate 124. The other end of upper back-up plate 124 is pressed towardlower back-up plate 126 by a plurality of springs 424a, only one ofwhich is shown in FIG. 5B. The back surface of upper bars 60a and 60bslides on a surface 426 as shown in FIG. 4 at the two lateral edges ofupper back-up plate 124. Also, as shown in FIG. 5B, lower back-up plate126 is fixedly supported at one end on threaded rods 404a and 404b (FIG.5A) by a plurality of nuts 406, 408 engaging the end of back-up plate126 and at the other end by a plurality of threaded rods, such as 410a,and by a plurality of nuts 412 and 414. The back surface of lower bars62a and 62b slides on a surface 416 as shown in FIG. 4 at the twolateral edges of lower back-up plate 126.

The back-up plates comprise a plurality of channels for providingcooling fluid to the back surfaces thereof. A description of thechannels will be made with reference to FIGS. 4 and 5B. The channelsinclude a fluid port 428a and 428b, an adjustable slot 430a and 430b anda groove 432a and 432b, formed in upper back-up plate 124 and lowerback-up plate 126, respectively. The channels also include a pluralityof exit ports 434a and 436a as shown in FIG. 5B formed in upper back-upplate 124 and exit ports 434b and 436b formed in lower back-up plate126. Fluid ports 428a and 428b are in fluid communication with groove432a and 432b, respectively, via adjustable slot 430a and 430b,respectively. Exit ports 434a and 434b and 436a and 436b are disposed influid communication with the ends of grooves 432a and 432b,respectively. Cooling fluid flows through port 428a, into groove 432avia slot 430a and out through exit ports 434a and 436a to cool the backsurfaces of upper bars 60a, 60b as shown in FIG. 4 which contact upperback-up plate 124. Similarly, cooling fluid flow through port 428b, intogroove 432b via slot 430b and out through exit ports 434b and 436b tocool the back surfaces of lower bars 62a, 62b which contact lowerback-up plate 126.

When pre-heating the web, it has been found that it is not sufficient toonly heat the material of the web and bring it into contact with a lowertemperature surface, such as that of the bars, to lock in the creases.The thermal inertial of a thin web is very low, so a heated web would bequenched too rapidly by a cooler surface before a sharp crease wouldform. If the web does not reach the deformation temperature upon contactwith the bars, the bending stress applied may be insufficient to sharplycrease the web. Later heating to the deformation temperature would thenproduce slack portions of web on the bars, and an inaccurate half-cellstructure would result. In order to prevent this, it is necessary toheat the bars to at least the deformation temperature of the web beforethe web is placed in contact with the bars. It is also necessary for thematerial of the web to immediately conform to sharp corners, such asthose shown at 68 and 70 in FIG. 4, of the half-cell forming apparatusbars upon contact and be held in the creased form at the web deformationtemperature for a brief moment before lowering the temperature to thestabilization temperature of the web. Therefore, the bars of thehalf-cell forming apparatus of the present invention must be cycled intemperature to the web stabilization temperature while the web is heldthereon to set the creases and then back to the web deformationtemperature so that it is ready for the next section of web. Inaddition, the web may be pre-heated to essentially the web deformationtemperature when contacting the bars at entry nip 106. For very thinwebs with low thermal inertia, pre-heating the web may not be necessary,as the web will rapidly reach the deformation temperature just bycontacting the bars. Heavier webs may require pre-heating.

The bars and the web are held at the deformation temperature for thetime they remain in enclosure 110. The bars and the web are lowered intemperature to the stabilization temperature of the material of the webafter leaving enclosure 110. Housing 128 is kept at a temperaturegenerally near the web stabilization temperature. The web should not bereleased from the bars until it has reached the stabilizationtemperature, or the bent form of the half-cell structure will not beaccurately retained. For an aramid paper, such as a paper made frompoly(m-phenylene isophthalamide), the deformation temperature is atemperature near or above the glass transition temperature and below atemperature that will thermally degrade or significantly discolor thepaper. The stabilization temperature is a temperature significantlybelow the deformation temperature, so that deformation of the half-cellstructure will no longer occur, but not so far below that reheating thebars is difficult. The stabilization temperature "locks in", or sets,the form of the bars in the web.

In addition, it is important that the web is placed on bars 60a, 60b,62a, 62b while under tension, and that tension is maintained on the webwhile it is held on the bars. The entrance tension on web 98 in FIG. 3as it enters the half-cell forming apparatus will not be transmittedthrough the web after it has passed over several bars, 60a, 60b, 62a and62b, as shown in FIG. 4, because of friction. For some webs, web tensiondevelops as the web contracts during cooling, but for other webs, thethermal expansion coefficient is low, so no appreciable contractionoccurs during cooling. For such webs, special methods of tensioning areachieved by back-up plates 124 and 126 as described above. The back-upplates ensure sharp corners, such as those shown at 68 and 70 in FIG. 4,are maintained in the half-cell structure, in spite of tolerancevariations in chains 70a, 70b, 72a, 72b, in bars 60a, 60b, 62a, 62b andin upper back-up plate 124 and lower back-up plate 126.

Half-cell structure forming apparatus 20 is set to run at a speed toallow sufficient time for heating the bars of the apparatus and the webto the deformation temperature of the web and for cooling the bars andthe web to the stabilization temperature of the web. The web entershalf-cell structure forming apparatus 20 at entry nip 106 as shown inFIG. 3 as a flat web of material under tension and exits as a supply ofhalf-cell structure under no tension, except that imposed by the freeweight of the exiting half-cell structure. The half-cell structure hangsunder its own weight as shown in FIG. 1 when it comes out of thehalf-cell forming apparatus.

In accordance with the present invention, there is provided a process ofmaking a honeycomb half-cell structure from a web of material. Theprocess comprises the steps of pre-heating a plurality of bars, such asbars 60a, 60b, 62aand 62b to at least the deformation temperature of theweb and contacting the outer surfaces of the bars with the web. The weband the bars are then cooled to the stabilization temperature of the webwhile holding the web on the bars. The web is then removed from thebars. The pre-heating step includes heating the web-contacting surfacesof the bars. In addition, the pre-heating step includes inductionheating the bars. Preferably, the entire web-contacting surfaces of thebars are induction heated. Additionally, the web may be pre-heatedbefore it is placed on the bars. The web is maintained under tensionwhile it is placed on the bars, as well as while it is held on the bars.

In accordance with the present invention, there is provided a processfor making a hexagonal-cell honeycomb core from a honeycomb half-cellstructure. The process comprises the steps of applying a first adhesivecomponent to a first group of peaks, applying a second adhesivecomponent to a second group of peaks and stacking the half-cellstructure so that the first adhesive component on the first group ofpeaks comes into contact with the second adhesive component on thesecond group of peaks, thereby mixing the components to bond thehalf-cell structure together and form the honeycomb core. This processis illustrated with reference to FIG. 6. FIG. 6 is an enlarged,perspective view of a portion of half-cell structure 25 which has beencoated with at least one adhesive. As noted above with respect to thedescription of FIG. 2, the peaks on one side of the half-cell structureare opposite valleys on the other side of the structure, and the valleyson the one side of the structure are opposite peaks on the other side ofthe structure. The step of applying the first adhesive componentcomprises applying the first adhesive component to the peaks on the oneside of the structure, such as those shown at 42 in FIG. 6. The step ofapplying the second adhesive component comprises applying the secondadhesive component to the peaks on the other side of the structure, suchas those shown at 42' in FIG. 6. In the present invention, the twoadhesive components are post-mixed after the half-cell structure isstacked, thereby allowing the two adhesive components of the adhesivesystem of the present invention to come into contact and cure to producea strong bond. The adhesive components remain sticky during theapplication thereof and during stacking to preserve the alignment of thesheets while the adhesive components cure.

The step of applying the first adhesive component comprises applying acyanate ester and an epoxy to the first group of peaks. A preferredfirst adhesive component is a combination of a cyanate ester such asArocy B-30, commercially available from Hi-Tek Polymers, a subsidiary ofRhone Poulenc, of Louisville, Ky., and an epoxy, such as Epoxy Epon 826,commercially available from Shell Chemical Company of Houston, Tex. Anyof the following is also suitable for the first adhesive component:epoxies, polyesters, polyimides, phenolics, polyureas, polyurethanes andbismaleimides. Any of the corresponding curing agents or catalysts forthe above list are suitable for the second adhesive component. A purposeof the epoxy in the first adhesive component is to reduce the viscosityof the cyanate ester. It also accelerates the cure of the adhesivesystem when heat is applied. The first component can cure by itself overa long time (several hours or days) or quickly (several seconds) when acatalyst is used and heat is applied. The step of applying the secondadhesive component comprises applying an epoxy and a catalyst to thesecond group of peaks. A preferred second adhesive component is acombination of the epoxy of the first adhesive component and a catalyst,such as zinc octoate soap. A purpose of the epoxy in the second adhesivecomponent is to increase the viscosity of the catalyst. Preferably, theepoxy is the same epoxy as that used in the first adhesive component;however, the epoxy may be a different epoxy.

In accordance with the present invention, there is provided ahexagonal-cell honeycomb core made by the process of applying the firstadhesive component to the first group of peaks and applying the secondadhesive component to the second group of peaks and stacking thestructure so that the first adhesive component on the first group ofpeaks comes into contact with the second adhesive component on thesecond group of peaks. In addition, there is provided a hexagonal-cellhoneycomb core made by the process of applying a cyanate ester and anepoxy to the first group of peaks and applying the epoxy and a catalystto the second group of peaks. Also, there is provided a hexagonal-cellhoneycomb core made by the process of applying the first adhesivecomponent to the peaks on one side of the structure and applying thesecond adhesive component to the peaks on the other side of thestructure.

In accordance with the present invention, there is provided a processfor making a hexagonal-cell honeycomb core from a honeycomb half-cellstructure. The process comprises the steps of applying a sticky adhesiveto the peaks of the half-cell structure and stacking the half-cellstructure while the adhesive remains sticky. The viscosity of the stickyadhesive of the present invention is at least 500 centipoise (cp)measured at the temperature at which the two sides of the half-cellstructure are joined together. The application step comprises applying afirst adhesive component 48 to a first group of peaks and applying asecond adhesive component 50 to a second group of peaks. The first groupof peaks is disposed on one side of the half-cell structure, such as theupper side of the half-cell structure, and includes the peaks coatedwith first adhesive component 48 as shown in FIG. 6. The second group ofpeaks is disposed on the other side of the half-cell structure, such asthe lower side of the half-cell structure, and includes the peaks coatedwith the second adhesive component 50 as shown in FIG. 6. The step ofapplying the first adhesive comprises applying a cyanate ester and anepoxy to the first group of peaks on one side of the structure, and thestep of applying the second adhesive comprises applying an epoxy, whichis preferably the epoxy of the first adhesive but which may be adifferent epoxy, and a catalyst to the second group of peaks on theother side of the structure. The half-cell structure is cut into aplurality of sheets while the adhesive on the peaks remains sticky. Thehalf-cell structure is cut across the diagonal surface. The sheets ofhalf-cell structure are then stacked. A hexagonal half-cell honeycombcore such as core shown at 30 in FIG. 2 is thus produced.

The advantages offered by the adhesive system of the present inventioninclude the following. The components do not set rapidly by themselves,so that there is adequate time after applying the adhesive to feed, cut,position and stack the sheets of half-cell structure. Also, eachcomponent has a long pot life, i.e., it does not degrade during the timeit is held at an elevated temperature in the adhesive-applying apparatusfor several hours during operation. In addition, the components arefluid enough (i.e., have a low viscosity) to spread in a thin layer, butare viscous enough not to run or drip. Furthermore, the components aresticky at the stacking temperature so the accurate position achievedduring stacking is immediately retained against small disturbing forcesuntil the adhesive components gel to form a strong bond. Also, thecomponents form a strong bond quickly (i.e., they have a fast gel timeof about one minute or less) when subjected to elevated temperatures.Each wet component has good adhesion with the honeycomb half-cellstructure, which makes a thin uniform coating which is easy to apply.Also, the set adhesive adheres well to the half-cell structure to createa strong bond. In addition, the cured adhesive has high temperatureresistance (i.e., a high glass transition temperature) of about 177degrees C.

Moreover, the adhesive system of the present invention is solvent-less.In systems using solvents, as the solvents evaporate between the twohalf-cell sheets at the bond, bubbles may form that decrease bondstrength. Also, the evaporated solvents may pose an environmental hazardthat must be contained and scrubbed. The adhesive system of the presentinvention thus has the advantage over other adhesives which must includesolvents to achieve low viscosity.

In addition, the adhesive system of the present invention is in aflowable, liquid form as the next sheet of half-cell structure is placedon the top of the core. This ensures that the adhesive components willmix properly and will flow into irregularities in the half-cellstructure peaks and form a large area for bonding where the peaks arepressed together. A thick layer of low-viscosity adhesive wastesadhesive, flows into undesirable parts of the apparatus and thehoneycomb core and produces a poor performance-to-weight product. Ahigh-viscosity adhesive does not fill irregularities and mix adequatelyfor a large area bond. If an alternate adhesive were used that is "dry",when the top half-cell sheet is placed on the honeycomb core, theadhesive may become sufficiently fluid to form a bond when heated, butthis requires time during which mis-registration may occur. It wouldalso require a higher pressure to produce a good contact bond, whichpressure may excessively deform the honeycomb core.

An alternate embodiment of the present invention is illustrated in FIGS.7A and 7B. This alternate embodiment includes the step of cutting thehalf-cell structure into a plurality of sheets. According to thisalternate embodiment, the step of applying a first adhesive componentincludes applying a first adhesive component 48' to the peaks on eachside of a first portion of the half-cell structure. The step of applyinga second adhesive component includes applying a second adhesivecomponent 50' to the peaks on each side of a second portion of thehalf-cell structure. The first and second adhesive components may be,but are not limited to the first and second adhesive components asdescribed above. The stacking step as shown in FIG. 7B includes cuttinga plurality of sheets from each portion and alternately placing a sheetfrom the first portion on a sheet from the second portion so that thepeaks of the sheets of the first and second portions come into contact,thereby mixing the first and second adhesive components together. Itshould be noted that the method according to this embodiment of thepresent invention may be practiced when the half-cell structure is acontinuous supply or is cut into sheets. Also in accordance with thepresent invention, there is provided a hexagonal-cell honeycomb coremade by the process described with respect to FIGS. 7A and 7B.

Another alternate embodiment of the present invention is illustrated inFIGS. 8A and 8B. In this alternate embodiment, the step of applying afirst adhesive component includes applying a first adhesive component48" to the peaks of one side of a first portion of the half-cellstructure and to the peaks of the other side of a second portion of thehalf-cell structure, where the first and second portions are separatedby a fold line. Also, the step of applying a second adhesive componentincludes applying a second adhesive component 50" to the peaks of theother side of the first portion and to the one side of the secondportion. As in the embodiment of FIGS. 7A and 7B, the first and secondadhesive components may be, but are not limited to, the first and secondadhesive components as described above. The stacking step includesfolding the half-cell structure so that the first and second portionsface each other and the first adhesive component on the peaks of thefirst and second portions is in contact with the second adhesivecomponent on the peaks of the first and second portions. This stackingstep is shown in FIG. 8B. Also in accordance with the present invention,there is provided a hexagonal-cell honeycomb core made by the processdescribed with respect to FIGS. 8A and 8B.

The above-discussed processes for applying at least one adhesivecomponent to half-cell structure may be implemented withadhesive-applying apparatus 24 as shown generally in FIG. 1. FIG. 9A isan enlarged, perspective view showing adhesive-applying apparatus 24 ingreater detail. The apparatus comprises at least one gravure roll forcoating the half-cell structure with at least one adhesive component. Agravure roll is shown at 138 in FIG. 9A. The at least one gravure rollincludes first gravure roll 138 as noted above for coating one side ofthe half-cell structure with the first adhesive component and a secondgravure roll 144 for coating the other side of the half-cell structurewith the second adhesive component. First gravure roll 138 is disposedin a first adhesive bath 43 which contains the first adhesive component.Second gravure roll 144 is disposed in a second adhesive bath 45 whichcontains the second adhesive component. First and second gravure rolls138 and 144 each has a plurality of pits 141 and 143, respectively,formed therein. The first adhesive component is held in pits 141 onfirst gravure roll 138, and the second adhesive component is held inpits 143 on second gravure roll 144. Preferably, the first and secondadhesive components are applied to the peaks of each side of thehalf-cell structure.

The apparatus also comprises means for positioning the half-cellstructure against the gravure roll. Preferably, the positioning means isresilient. Also preferably, the positioning means comprises at least oneback-up roll. A back--up roll is shown at 130 in FIG. 9A. Back-up roll130 includes a plurality of bars 137 on the surface thereof forsupporting the half-cell structure. A space 127 is formed between eachconsecutive bar 137. In addition, the positioning means may comprise anyother device for positioning half-cell structure against a gravure roll,including, but not limited to, a transfer head or a belt with teeth onit. The positioning means may also comprise a second back-up roll 132for positioning the half-cell structure against the second gravure roll.Back-up roll 132 includes a plurality of bars 139 on the surface thereoffor supporting the half-cell structure against second gravure roll 144.A space 129 is formed between each consecutive second bar 139.Preferably, first and second back-up rolls 130 and 132 are resilient;specifically, bars 137 and 139 are resilient. The depth of the spaces ofthe first and second back-up rolls is greater than the height of peaks42 on the half-cell structure. Back-up rolls 130 and 132 contact thehalf-cell structure at a contact surface 120 and are relieved aroundspaces 129 as shown in FIG. 9B. The peaks on one side of the half-cellstructure face away from bars 137 of first back-up roll 130.

Referring to FIG. 9B, this arrangement of contacting the half-cellstructure at valleys 44 and not contacting it at peaks 42 is importantto ensure uniform support at surface 120 and therefore a uniform coatingof adhesive. Space 129 must provide clearance so second back-up roll 132does not contact adhesive coating 48 on peak 42. Even when an adhesivecoating is absent (as it is on first back-up roll 130), if space 129matched the theoretical profile of peak 42 and diagonal surfaces 46, theactual height of the peak would vary from the theoretical, so a perfectmatch would not always occur. If peak 42 were higher than the "matching"depth of space 129, valley 44 would not fully engage contact surface120, and uniform application of adhesive to peak 42' would not occur.

The peaks on the half-cell structure face away from the bars of eachrespective back-up roll, and the peaks contact each respective first andsecond gravure roll so that the first adhesive component contacts thepeaks on the one side and the second adhesive component contacts thepeaks on the other side to apply the first and second adhesivecomponents to the half-cell structure. Specifically, valleys 44 on theone side of the half-cell structure are placed in contact with the barson second back-up roll 132; peaks 42' on the other side of the half-cellstructure face away from bars 139 on second back-up roll 132. Also,valleys 44' on the other side of the half-cell structure are placed incontact with the bars on first back-up roll 130; peaks 42 on the otherside of the half-cell structure face away from bars 137 on first back-uproll 130. Accordingly, the first adhesive component contacts the peakson the one side and the second adhesive component contacts the peaks onthe other side of the half-cell structure to apply the first and secondadhesive components to the half-cell structure.

First and second back-up rolls 130 and 132, respectively, are driventogether at the same speed through suitable gearing by a motor 452. Amotor 454 drives first gravure roll 138, and a motor 456 drives secondgravure roll 144, so that the first and second gravure rolls are drivenseparately. The gravure rolls are preferably driven at the same speed asthe back-up rolls. First gravure roll 138, first adhesive bath 43 andmotor 454 are attached to a carriage 455 for reciprocation by a cylinder457 in the direction of arrow 458 to press toward and away from back-uproll 130. Second gravure roll 144, second adhesive bath 45 and motor 456are similarly disposed for movement in the direction of arrow 460 topress toward and away from back-up roll 132. When the gravure rolls areretracted from the back-up rolls, they can be independently driven bytheir respective motors 454 and 456 to agitate their respective adhesivebaths.

A differential pressure system is shown at 436 in FIG. 9A and includes avacuum source 437 and a pressure source 462. A vacuum is applied at eachof spaces 127 and 129 through at least one vacuum hole 131, as shown inFIG. 9B only, on back-up roll 132 to hold the half-cell structureagainst or separate it from the first and second back-up rolls. Byproviding the vacuum holes on the non-contacting portion of the back-uprolls, the peaks of the half-cell structure are not deformed on contactsurface 120, as they might be if the vacuum holes were located there.This is important to achieve good contact between the entire area of thepeaks and the adhesive on the pitted surface of the first and secondgravure rolls. The back-up rolls are in fluid communication with vacuumsource 436 over about 270 degrees of rotation and with pressure source462 over about 90 degrees of rotation, as determined by a pair ofnon-rotating partitions 134 and 136 formed within the back-up rolls. Theelevated pressure ensures the half-cell structure is positivelyseparated from the back-up rolls when the vacuum is removed at thepartitions.

As shown in FIG. 9A, the half-cell structure is held tightly on back-uprolls 130 and 132 and is brought into contact with gravure rolls 138 and144, respectively. Gravure roll 138 has a peripheral surface 140 and isdisposed in contact with bath 43 of the first component of the two-partadhesive. Gravure roll 144 has a peripheral surface 145 and is disposedin contact with bath 45 of the second component of the two-part adhesivesystem. Peripheral surface 140 of gravure roll 138 is coated with a filmof the first component, and peripheral surface 145 of gravure roll 144is coated with a film of the second component. A doctor blade 142 wipesperipheral surface 140 of gravure roll 138 clean, leaving the adhesivecomponent only in pits on the surface of gravure roll 138. A doctorblade 147 similarly wipes peripheral surface 145 of gravure roll 144.This arrangement accurately controls the adhesive thickness, and thuscontrols the quantity of the adhesive applied to the half-cellstructure. The thickness of the layers of the first adhesive componentand the second adhesive component, respectively, applied by theadhesive-applying apparatus of the present invention may be the same,but do not necessarily have to be so. The discrete spots of the adhesivecomponents transferred to the half-cell structure by theadhesive-applying apparatus of the present invention coalesce into acontinuous film, or areas of film, as the half-cell structure leavesgravure rolls 138 and 144.

As noted above, back-up rolls 130 and 132 are preferably made of aresilient material, such as rubber. Gravure rolls 138 and 144 are formedfrom a non-elastic metal. Thus, resilient back-up rolls 130 and 132 canbe brought into pressing contact with non-resilient gravure rolls 138and 144, respectively, and intimate contact between the half-cellstructure and each gravure roll is assured. This arrangement controlsthe uniformity of the application of the adhesive.

As the half-cell structure is pressed against the surfaces of gravureroll 138, it contacts pools of the first adhesive component whichcollect in the pits of the roll, and the component is transferred to thepeaks of the half-cell structure. As the half-cell structure leavesfirst back-up roll 130, it is inverted so that the top of the half-cellstructure is facing second back-up roll 132. This allows the peaks onthe other side of the half-cell structure to come into contact with thesecond adhesive component on the surface of gravure roll 144. Theadhesive-coated half-cell structure is released from second back-up roll132 and is guided into an unsupported loop, shown near the bottom ofFIG. 9A. The continuous half-cell structure leaving adhesive applyingapparatus 24 has sticky adhesive applied to the top and bottom peaks,and therefore these surfaces cannot be touched. The half-cell structureis released from vacuum source 437 and is guided and supported with aflow of air from a slot jet 438. The half-cell structure falls into afree loop as shown near the bottom of FIG. 9A. A sensor 440 detects thepresence or absence of the loop. Sensor 440 is connected to distributedcontrol system 38 as shown in FIG. 1.

In accordance with the present invention, there is provided a process ofapplying at least one adhesive component to a continuous supply ofhoneycomb half-cell structure. The process comprises the step ofdirecting the half-cell structure to at least one gravure roll, such asfirst gravure roll 138 and second gravure roll 144. The process alsocomprises the step of positioning the half-cell structure against thegravure roll.

The process of the present invention further includes the steps ofdirecting the half-cell structure through a wrap around a first back-uproll in a first direction and directing the half-cell structure througha wrap around a second back-up roll in a second direction. Preferably,the half-cell structure is directed through at least a 90 degree wrap inthe first direction and through at least a 90 degree wrap in the seconddirection.

The positioning step of the present invention includes the sub-step ofplacing the valleys on one side of the half-cell structure in contactwith a plurality of bars formed on the second back-up roll, where thepeaks on the other side of the structure face away from the bars on thesecond back-up roll. The placing step includes placing the peaks on theone side of the structure in a space formed between the bars of thesecond back-up roll. The positioning step also includes the sub-step ofplacing the valleys of the other side of the structure in contact with aplurality of bars formed on the first back-up roll, where the peaks onthe one side of the structure face away from the bars on the firstback-up roll. The placing step includes placing the peaks on the otherside of the structure in a space formed between the bars of the firstback-up roll, where the width of the spaces of the first and secondback-up rolls is about the distance between adjacent valleys of thehalf-cell structure, and the depth of the space is greater than theheight of the peaks.

The process of the present invention further includes the step ofplacing a first adhesive component on a first gravure roll, such asgravure roll 138, and placing a second adhesive component on a secondgravure roll, such as gravure roll 144. The first and second adhesivecomponents may be, but are not limited to, the first and second adhesivecomponents as described above. Specifically, the first adhesivecomponent is placed in a plurality of pits, such as pits 141, extendingbelow the surface of the first gravure roll. The second adhesivecomponent is placed in a plurality of pits, such as pits 143, extendingbelow the surface of the second gravure roll. The peaks of the one sideof the structure are then pressed between the first back-up roll and thefirst gravure roll, thereby contacting the first adhesive component withthe peaks on the one side. Also, the peaks on the other side of thestructure are pressed between the second back-up roll and the secondgravure roll, thereby contacting the second adhesive component with thepeaks on the other side to apply the first and second adhesivecomponents to the half-cell structure. The half-cell structure is heldagainst a first back-up roll, such as 130, and a second back-up roll,such as 132, by a vacuum. The vacuum is applied to the spaces, such as127 and 129, between the bars on the first and second back-up rolls.

As noted above, system 10 comprises cutting apparatus 26 for cutting thesupply of half-cell structure into a plurality of sheets. The cuttingapparatus of the present invention comprises means for cutting thehoneycomb half-cell structure into a plurality of sheets. Preferably thecutting means comprises a blade 157 as shown in FIGS. 1 and 10A-C. Blade157 comprises a razor blade which is coated with tungsten carbide orboron nitride for wear resistance. Blade 157 is guided across thehalf-cell structure by a conventional slide mechanism driven by an aircylinder. Alternatively, a wire cutter, a laser or a water jet or thelike could be used as the cutting means. An alternate cuttingarrangement to that of the present invention is a rotary cutterconsisting of a disc rotated by an electric or air motor, so that alonger lasting cutting surface is available.

The cutting apparatus of the present invention also comprises means forpositioning a length of the half-cell structure. Preferably, thepositioning means comprises a conveyor 28 as shown in general in FIG. 1and in greater detail in FIGS. 10-13 which positions a length ofhalf-cell structure. The positioning means could also comprise any othermechanical, electrical, or electro-mechanical device or mechanism whichaccurately positions a length of half-cell structure and prepares it forcutting. The sheets are positioned for cutting across the diagonalsurface as shown at line 150 in FIG. 6.

Further in accordance with the present invention, there is provided aprocess for cutting a honeycomb half-cell structure into a plurality ofsheets. The process comprises the steps of positioning a length of thecontinuous supply of half-cell structure on a conveyor so that thediagonal surfaces of the half-cell structure are positioned adjacent ablade for cutting. The process also comprises the step of cutting acrossthe diagonal surface to form the sheets. The process further includesthe step of stacking the sheets onto each other so that the peaks on oneside of a sheet contact the peaks on the other side of an adjacent sheetto form a honeycomb core. Accordingly, there is also provided ahexagonal-cell honeycomb core, such as that shown at 30 in FIG. 2, madeby the process of cutting the structure across the diagonal surfacesthereof to form a plurality of sheets and stacking the structure byplacing a sheet with the peaks on one side of the sheet in contact withthe peaks on the other side of an adjacent sheet.

Referring again to FIG. 9A, adhesive-coated half-cell structure 25 mustbe guided onto the top, flat portion of conveyor 28. The half-cellstructure, which is coated with sticky adhesive, should be preventedfrom touching any surface. For this purpose, an air bar 442 and a pairof transparent side plates 444 and 446 as shown in FIG. 9A are attachedto a conveyor frame 304 and a guard 305 as shown in FIG. 13, which inturn is mounted to conveyor frame 304. Frame 304 is shown in particularin FIGS. 12 and 13 and is the stationary part of the conveyor. Plates444 and 446 guide and support the half-cell structure without contactingthe sticky adhesive on the peaks. Plates 444 and 446 are spaced slightlyfurther apart than the width of the half-cell structure. Air bar 442 hasa plurality of holes 448 centrally located on its surface which are influid communication with a source of pressurized air, such as an airblower 449 as shown in FIG. 9A. When the loop is sensed by sensor 440,conveyor 28 advances the half-cell structure a fixed length and stops toallow cutting of a sheet of the half-cell structure. While the conveyoris stopped, the loop descends as the half-cell structure is advanced byadhesive applying apparatus 24, until the loop is detected by sensor440. The conveyor is advanced again, or the adhesive applying apparatusis slowed or stopped if the conveyor cannot advance.

The conveyor comprises a plurality of connected platens 139 and 145 asshown in FIGS. 10A-10C and FIG. 11 which support the half-cellstructure. Platens 139 and 145 ride on a U-shaped channel 302 as shownin FIGS. 12 and 13 which is fastened to frame 304 and which has a platenmanifold 175 provided therein. A plurality of surfaces 181 and 183 areprovided on channel 302 for supporting platens 139 and 145. Platens 139and 145 are connected at a pivot 146 as shown in FIGS. 10B and 10C.Platens 139 and 145 comprise a plurality of support bars, such as141a-141f as shown in FIGS. 10A-10C, which have about the same pitch asbars 60a, 60b, 62a and 62b of half-cell forming apparatus 20. Aplurality of spaces, such as 143a and 143b, is formed between eachconsecutive bar as shown in FIGS. 10A-10C. Support bars 141a-141f of theplatens contact the valleys on the other side, or bottom, of thehalf-cell structure.

The cutting apparatus of the present invention incorporates specialconsiderations to achieve accurate alignment of adjacent sheets ofhalf-cell structure when they are stacked on top of each other. Thenumber of bars on each consecutive platen alternates between an odd andan even number. In the preferred embodiment, conveyor platens 139 and145 are 101/2 pitches long from pivot to pivot as shown at 133 and 135,respectively, in FIG. 10A. The platens have different numbers of barsand spaces. For example, platen 145 may have 10 bars and 11 spaces, suchas 141a and 143b, respectively, and platen 139 may have 11 bars and 10spaces. The conveyor index in the direction as designated by arrow 151as shown in FIG. 10B is constrained to be an odd number of platens toachieve the one-half pitch increment, so that blade 157 alternately cutsfirst on one side of a first predetermined bar, such as a downstreamside, as illustrated at 147 in FIG. 10B and then on one side of a secondpredetermined bar, such as an upstream side, as illustrated at 149 inFIG. 10C. The blade remains fixed along the conveyor, and the conveyoradvances a repeatable distance. This distance must always be equal to aninteger plus one-half of the pitch of the half-cell structure. Stackerarm 31 must move back and forth laterally one-half pitch, as betweenpoints 153 and 155 in FIGS. 10B and 10C, to pick up alternate sheets ofhalf-cell structure.

Platens 139 and 145 are connected in an endless chain 300 whichcomprises support bars 141a-141f. Platens 139 and 145 are driven andsupported by a chain idler sprocket 33 and a chain drive sprocket 35 asshown in FIG. 12. A shaft 306 is supported on frame 304 and holds chainidler sprocket 33. A shaft 308 is also supported on frame 304 and holdschain drive sprocket 35. A drive motor/gear reducer 310, shown attachedbehind frame 304, drives shaft 308. The motor of motor/reducer 310 is aDC servo-motor that can be precisely controlled. A tensioner 312 and aplurality of support rollers 314, which are attached to frame 304, keepchain 300 taut. As shown in FIG. 12, a drag brake mechanism 299 isattached to frame 304 and acts on idler sprocket 33 to keep chain 300under tension as it advances.

Blade 157 is provided near the inlet end of conveyor 28 as shown inFIG. 1. When sensor 440 as shown in FIG. 9A senses half-cell structure25, conveyor 28 moves to the right as shown in FIG. 1. For example, theconveyor moves to the right a distance of 2201/2 half-cell structurepitches, which pulls about 1.2 meters of continuous half-cell structureout of the loop at the exit end of adhesive-applying apparatus 24. Theconveyor then stops, and blade 157 traverses the half-cell structureacross space 143b between two adjacent support bars 141a and 141b asshown in FIGS. 10A and 13, where the advanced blade is shown at 157'.This cuts the half-cell structure at a position as shown at line 150 inFIG. 6 midway between a peak and a valley across a diagonal surface ofthe half-cell structure, so a discrete sheet of half-cell structure canbe picked up by stacker arm 31. Stacker arm 31 then moves over thesheets on the conveyor and stops closely spaced from the sheets.Conveyor 28 ensures that the continuous half-cell structure isaccurately positioned for cutting into sheets by blade 157 and that thecut sheet is positioned for pick-up by stacker arm 31. Accurate stoppingof the conveyor with the half-cell structure held on bars 141a-141d ofthe platens is particularly important so that the half-cell structure iscut along the diagonal surface. This positioning must be independent oftolerance accumulation from bar to bar and platen to platen, independentof wear that would effect the dimension between platens, and independentof platen and drive motor inertia and friction variables.

The honeycomb half-cell structure is cut into sheets after the adhesiveis applied and while the adhesive is still wet and sticky. The cutoccurs across diagonal surface 46 between the adhesive-coated peaksalong line 150 so that the blade does not contact the adhesive andbecome covered with wet, sticky adhesive that would prevent accuratecutting. It should be noted that the cut along the diagonal surface ofthe present invention is not dependent on the application of adhesive.In either case where adhesive is or is not applied, cutting thehalf-cell structure along the diagonal surface achieves the advantage ofpreventing waste of half-cell structure. A cut can be made at thebeginning of one sheet and at the end of the next sheet after advancingby a distance equal to an integer plus one-half the pitch of thehalf-cell structure so that the edges line up, and no trimming isnecessary. In addition, there is no need to flip the sheets of half-cellstructure with the present invention, which reduces operation time andcost, while still having the ends of the sheets align for accurateguiding in the stack holder. Cutting on the diagonal surface of thehalf-cell structure also eliminates the possibility of getting adhesiveon the blade or on the end guides for each sheet as they are stacked,since adhesive is never applied to the diagonal surfaces. In contrast,when cuts are made on the surfaces where adhesive is applied, the blademust cut through the adhesive, thereby accumulating adhesive, which mustperiodically be cleaned off. Also, as the cut sheet is stacked, the endsof the sheets which are cut along the bond area curl up as they contactend guide plates. This curling up exposes the adhesive to the end guideplates, which causes sticking of the sheet and/or contaminates theplates for the next sheet.

The apparatus of the present invention, by sensing the position of thebars in conjunction with controlling the motor speed of the conveyor,ensures accurate stopping and positioning of the half-cell structure forcutting. Thus, in accordance with the present invention, the means forpositioning the half-cell structure for cutting comprises means foralternately positioning a bar adjacent one side of the cutting means andthe other side of the cutting means to cut across the diagonal surfacesof the structure. Preferably, the means for alternately positioning abar comprises a plurality of sensors 316, 318, 320, 322, 324, a motor ofmotor/reducer 310, a rotary encoder 298 as described below anddistributed control system 38 as described above. Alternatively, themeans for alternately positioning may comprise any mechanical orelectrical mechanism for positioning a bar on the conveyor. As shown inFIG. 11, conveyor 28 is provided with a platen sensor 316, a pluralityof bar sensors 318 and 320 for sensing where to stop a 10-bar platen,such as platen 145, and a plurality of bar sensors 322 and 324 forsensing where to stop an 11-bar platen, such as platen 139. All ofsensors 316, 318, 320, 322 and 324 are mounted on channel 302. As shownin FIG. 13, sensor 316 is mounted on channel 302 at an elevation so itsees a trailing edge 317 of a platen; bar sensors, such as 318 as shownin FIG. 13, are mounted on channel 302 at an elevation so they see anedge 319 of the bars on each platen. During advancing of the continuoushalf-cell structure, chain 300 is traveling at high speed, so it must beslowed before stopping. Conveyor 28 is indexed the approximate distanceof a sheet, as determined for instance by rotary encoder 298, which isdisposed on shaft 308 as shown in FIG. 12. The motor of motor/reducer310, encoder 298 and sensors 318, 320, 322 and 324 are operativelyconnected to distributed control system 38. Sensor 316 senses when thetrailing edge of the platen preceding the one for cutting has passed.When sensor 316 senses the trailing edge of the last platen precedingthe one where cutting is to occur, the motor of motor/reducer 310 iscommanded by distributed control system 38, as shown in FIG. 1, to runat a slow speed. Sensor input from all sensors is then monitored. If thedistributed control system expects to cut on a ten-bar platen, sensors318 and 320 will both be "on" when sensor 318 sees the leading edge ofbar 141c and sensor 320 has not yet seen the space beyond the trailingedge of bar 141d several bars away. The choice of which bars to look atdepends on the space available on channel 302 for mounting and adjustingthe sensor hardware. At this point, the motor of motor/reducer 310 iscommanded to stop. When stopped, bars 141a and 141b on platen 145downstream of the sensors are properly positioned at the blade forcutting across the diagonal surface of the half-cell structure at theupstream side of bar 141a on platen 145 as shown in FIG. 10B. The use oftwo bar sensors and a platen sensor for determining when to stop theconveyor is useful for providing a large margin of variability forresponse of distributed control system 38 to the sensors. In addition,they can detect malfunctions of the conveyor if sensor 320 sees beyondthe trailing edge of a bar, which indicates the conveyor has moved toofar and is inaccurately positioned for cutting. If a very fast controlsystem were used, only one sensor, such as sensor 316 which senses theedge of a platen, could be reliably employed to stop the conveyoraccurately, and other means could be used to detect malfunctions.

With the conveyor accurately stopped, the blade can cut across thehalf-cell structure on 10-bar platen 145, thereby separating a sheet ofhalf-cell structure and making it available for stacking. When thissheet is transferred to the stacking apparatus, the conveyor is free toadvance the half-cell structure forward one sheet length again byindexing a plurality of platens and this time stopping at an 11-barplaten 139. To stop at an 11-bar platen, sensors 322 and 324 areemployed in conjunction with platen sensor 316 to monitor the positionof a different pair of bars, which are at a different position spacedone-half pitch of the half-cell structure away from the bars sensed bysensors 318 and 320 used on the previous stop. The process for stoppingis the same as previously described, except sensors 322 and 324 areemployed instead of sensors 318 and 320. When stopped, bars 141a and141b on 11-bar platen 139 downstream of the sensors are properlypositioned at the blade for cutting across the diagonal surface at theupstream side of bar 141b on platen 145 as shown in FIG. 10C.

The cutting apparatus of the present invention further includes adifferential pressure system for holding the half-cell structure on theconveyor while advancing the half-cell structure and cutting thecontinuous structure into sheets and for disengaging the sheets from theconveyor during pick-up by stacker arm 31. The differential pressuresystem is shown generally at 334 in FIG. 1. and includes, as shown inFIG. 12, a plurality of pressure sources 336a-c, valves 338a-c, blow-offvents 330, 331 and 332, vacuum sources 341a-c, valves 343a-c and vacuumports 171, 173 and 333. Pressure sources 336a, 336b and 336c areconnected to valves 338a, 338b and 338c, respectively, for controllingthe air flow therefrom to blow-off vents 332, 331 and 330, respectively.Vacuum sources 341a, 341b and 341c are connected to valves 343a, 343band 343c, respectively, for controlling the vacuum thereto to vacuumports 333, 173 and 171, respectively. Valves 343a-c and 338a-c arecontrolled by distributed control system 38. For explanation, only threevacuum ports and three blow-off vents are described, but more or lesscould be used. Each vacuum source can be a separate vacuum blower orpump, or a single pump can be manifolded to all of valves 343a-c.Similarly, each pressure source can be a separate compressor or blower,or a single compressor can be manifolded to all of valves 338a-c. Thevacuum applied through ports 171, 173 and 333 holds the half-cellstructure on the conveyor until the structure is cut and stacker arm 31is ready to pick up the cut sheet, at which time the vacuum appliedthrough ports 171 and 173 is turned off and the pressure to blow-offvents 330, 331 and 332 is turned on to transfer the sheet to the stackerarm. The vacuum applied through port 333 remains on continually to holdthe leading edge of the half-cell structure on the conveyor.

At least one of spaces 143a formed between platen bars 141e and 141fincludes an opening disposed in fluid communication with thedifferential pressure system. The opening may comprise a plurality ofports 159 as shown in FIGS. 10A and 10B. Clearances associated withjoints 146 between platens also act as ports. Preferably, at least onespace has at least one port formed in the bottom surface thereof, andthe port is in communication with the differential pressure system. Asshown in FIG. 10A, ports 159 are formed in the bottom of the spaces. Thespaces between the bars comprise at least one cutting space 143b asshown in FIG. 10A, and the blade and the cutting space are disposed inhorizontal alignment when the bar is positioned at the blade. A vacuumfrom differential pressure system 334 is applied through ports 159 ineach space on both sides of cutting space 143b. Preferably, the vacuumsource is applied only through the ports in each space on both sides ofthe cutting space. If there is a vacuum applied at the space where thecut is made, it would pull the cut end down after cutting, so the stickyadhesive-coated peak would contact the side of a bar and would stickthere, which is undesirable.

The plurality of vacuum ports 171, 173 and 333 and the plurality ofblow-off vents 330, 331 and 332 are shown in FIGS. 11 and 12 mounted tochannel 302 and are in fluid communication with platen manifold 175. Abaffle 335 is provided in manifold 175 as shown in FIG. 12 to shield theeffects of adjacent blow-off vent 332 from the vacuum supplied by vacuumport 333. This arrangement of individually controlled vacuum ports andblow-off vents permits independent off-on operation of each vacuum portand blow-off vent without losing control of the leading edge of thecontinuous half-cell structure.

In accordance with the present invention, there is provided a processfor cutting a honeycomb half-cell structure into a plurality of sheets.The process comprises the steps of positioning a length of the half-cellstructure so that the diagonal surfaces of the half-cell structure arepositioned for cutting adjacent a blade, such as blade 157, and cuttingthe half-cell structure across the diagonal surface to form the sheets.The half-cell structure is cut across the diagonal surface alternatingbetween one side and the other of a predetermined bar, such as platenbars 141a and 141b. The half-cell structure is positioned on a conveyor,such as conveyor 28 as described above, and the conveyor is advanced byan integer number plus one-half of the pitch of the half-cell structure.A vacuum, such as that from vacuum sources 341a-c, is applied to thehalf-cell structure via ports 159 to hold the half-cell structure inplace while it is cut and advanced. The structure is placed on theconveyor, which, as described above, has a plurality of bars, such as141a-141d, which contact the valleys on one side of the half-cellstructure and a space, such as 143a and 143b, between each consecutivebar. At least one of the spaces comprises a cutting space, such ascutting space 143b, which is disposed in horizontal alignment with theblade when the conveyor stops advancing. The conveyor is stopped at thecutting space, and the vacuum is applied through the ports in each spaceadjacent the cutting space. It is preferable that the vacuum is appliedonly through the ports in each space on both sides of the cutting space.

Further in accordance with the present invention, there is provided ahoneycomb core made by positioning the half-cell structure so that thediagonal surfaces of the half-cell structure are positioned adjacent ablade for cutting and by cutting the half-cell structure across thediagonal surface to form the sheets. This core is illustrated in FIG. 2as described above, where cut diagonal surfaces 46, 46' of the sheetsare aligned at the edge of the core at 297 as a direct result of theassembly process.

The principles employed in the conveyor of the present invention may beextended to any system for advancing the leading edge of a supply ofcorrugated web, which may be other than honeycomb half-cell structure.Thus, in accordance with a further embodiment of the present invention,there is provided a system for advancing the leading edge of a supply ofcorrugated web which has a plurality of alternating peaks and valleys,where the system positions the web for a secondary operation. Such asystem is shown generally at 28 in FIGS. 11 and 12. The secondaryoperation may include a cutting operation to cut a discrete sheet fromthe web, such as that performed by blade 157 as described above. Othersecondary operations may replace the cutting operation or be in additionto the cutting operation, such as a marking operation, anadhesive-applying operation or a folding operation.

The advancing system of the present invention comprises endless loopconveying means including a plurality of spaced support bars forcontacting the valleys of the web, where the conveying means has anentrance end and an exit end. Preferably, the conveying means comprisesa conveyor, such as conveyor 28 as described above and as shown in FIGS.1 and 10-13, which includes spaced support bars, such as 141a-141f asdescribed above, for contacting the valleys of the web. In the advancingsystem of the present invention, it is preferable that they contact onlythe valleys of the web. A space, such as spaces 143a and 143b asdescribed above, is formed between each consecutive bar. The space has adepth greater than the height of each peak of the web. The conveyor ofthe advancing system of the present invention comprises a plurality ofplatens, such as platens 139 and 145, where the support bars are formedon the platens. The number of bars on each consecutive platen alternatesbetween an odd and an even number.

The advancing system of the present invention further includes holdingmeans for holding the web against the support bars. Preferably, theholding means comprises at least one vacuum source, such as vacuumsources 341a-c as described above, for holding the web against supportbars 141a-f. The advancing system of the present invention also includesmeans for disengaging the web from the support bars. Preferably, thedisengaging means comprises at least one pressure source, such aspressure sources 336a-c, for disengaging the web from support bars141a-141f. The advancing system of the present invention furtherincludes means for selectively activating and de-activating the holdingmeans and the disengaging means to remove the cut sheet of web from thesupport bars. Preferably, the means for selectively activating andde-activating the holding means and the disengaging means comprises aplurality of valves 338a-c and 343a-c, which function as describedabove.

The advancing system of the present invention also comprises advancingmeans for repeatedly advancing the conveying means and the leading edgeof the web from the entrance end of the conveying means to the exit endthereof. The advancing means preferably comprises a motor, such as themotor of motor/reducer 310 as described above, and a distributed controlsystem, such as distributed control system 38 as described above. Theadvancing system of the present invention also comprises stopping meansfor repeatedly stopping the advancing means after a predetermined numberof support bars have advanced past a position for applying the secondaryoperation to the web. Preferably, the stopping means comprises a rotaryencoder, such as rotary encoder 298 as described above, and a sensor,such as any one of sensors 318, 320, 322 and 324 as described above, forsensing the presence of a support bar near the position for applying thesecondary operation. The motor, the encoder and the sensor of theadvancing system of the present invention are operatively connected todistributed control system 38.

In accordance with the present invention, there is provided a method ofadvancing the leading edge of a supply of corrugated web having aplurality of alternating peaks and valleys and of handling the web for asecondary operation. The method comprises the step of engaging theleading edge of the web at an entrance end of a conveyor, such asconveyor 28 as described above. The entrance end of the conveyor can beanywhere from near idler sprocket 33 where the web first contacts theconveyor to just adjacent the secondary operation, such as adjacentblade 157 as shown in FIG. 12. The leading edge of the web is advancedas the leading edge moves from the entrance end to an exit end of theconveyor a distance equal to an integer plus one-half the pitch of theweb. The conveyor is advanced by a distance equal to an odd number ofconveyor platens. The valleys of the web contact a plurality of supportbars formed on the conveyor for supporting the advancing web. It ispreferable that only the valleys of the web contact the support bars.The advancing web is held against the support bars and is stopped toposition the web adjacent the secondary operation at the entrance end ofthe conveyor. The secondary operation includes cutting a discrete sheetfrom the web, such as with blade 157.

The holding step includes activating at least one vacuum source, such asvacuum sources 341a-c. The method of the present invention furtherincludes the step of deactivating the vacuum source to release the cutsheet from the conveyor, and activating at least one pressure source,such as pressure sources 336a-c, to remove the cut sheet from theconveyor. The activating and the de-activating steps are doneprogressively from one end of the conveyor to the other to progressivelyremove the cut sheet from the conveyor.

In accordance with the present invention, there is provided a transferhead for holding a sheet of honeycomb half-cell structure. Referring toFIGS. 10B, 10C and 14A, stacker arm 31 includes an extension rod 31a anda transfer head 31b attached to the extension rod. Extension rod 31aisattached to and is moved by a cylinder mechanism 31c as shown in FIG. 1for motion between a pick-up position 344 at conveyor 28 and a depositposition 345 at stack holder 32. Cylinder 31c is supported by conveyorframe 304. Transfer head 31b comprises a plurality of support bars 162and 163 that support the sheets of half-cell structure along the valleysthereof and provide clearance with the peaks of the sheets, as do thebars of the forming apparatus and the conveyor. At least one space 161is formed between each support bar, where the width of each space isabout the distance between adjacent valleys of the half-cell structureand the depth of the space is greater than the height of the peaks.Within each bar are ports 164 and 165 spaced along the length of eachbar in fluid communication with a transfer head manifold 166. Manifold166 is disposed in transfer head 31b as shown in FIG. 10B. The transferhead of the present invention also includes a differential pressuresystem for holding the sheets against the support bars and disengagingthe sheets therefrom. The differential pressure system comprises avalved vacuum source 167 and a valved pressure source 168 as shown inFIG. 15. Manifold 166 is in fluid communication with vacuum source 167or pressure source 168, so that the sheets of half-cell structure canalternately be held securely by vacuum to bars 162 and 163 or blown offthe bars by pressure.

At the end of extension rod 31a is a two-axis shift mechanism 301 asshown in FIGS. 14A and 15 that moves transfer head 31b up and down andside to side relative to rod 31a. The up position is used to receive thehalf-cell sheet from the conveyor, and the down position is used toplace the sheet on the top of the stack of sheets of the core. Duringthe travel between the conveyor and the stacking apparatus, transferhead 31b is in the up position. The side positions shift the head byone-half of a half-cell pitch in the preferred embodiment to pick upalternate half-cell sheets from the 10-bar and 11-bar platens on theconveyor and place them in the stacking apparatus.

Chain 300, which comprises platens 139 and 145 with bars 141a-141f, musthave clearances so that the platens pivot freely relative to each otherat pivot 146 as they travel around sprockets 33 and 35. There is somevariation in dimensions from pivot to pivot and in the clearances at thepivots. Such pivots also eventually wear, and the tolerances andclearances may change. These variations may cause slight differencesbetween the pitch of chain 300 compared to the pitch of transfer head31b. If transfer head 31b were to be lowered into the spaces betweenchain platen bars to pick up the half-cell structure by engaging thevalleys, there may be mechanical interferences between bars 162 and 163on the transfer head and bars 141a-141f on the platens caused by thesevariations. To avoid this, transfer head 31b remains in a position aboveplaten support bars 141a-141f, and the cut sheet of half-cell structureis blown off platen chain 300 and sucked onto the transfer head.

When it is desired to transfer a sheet of half-cell structure from theconveyor to the transfer head, the transfer head is positioned above theconveyor, and distributed control system 38 begins the transfer of thesheet. The present invention employs a progressive transfer of the sheetof half-cell structure from platen support bars 141a-141f to transferhead bars 162, 163 by sequential vacuum release and pressure blow-offfrom one vacuum zone to the next along the conveyor. Transfer headvacuum 167 is turned on to receive the sheet. The first step in thetransfer process of the present invention is to turn off vacuum to port171 and to simultaneously turn on vents 330 and 331. This blows off theend of the sheet, which is positioned as shown at 342 in FIG. 12 at thedrive end of conveyor 28, and the sheet moves up and is captured by thevacuum on transfer head 31b created by vacuum source 167 over thatportion of the sheet. The next single vent and port are de-activated andactivated to blow up the next portion of sheet and so on until, at theend of the conveyor where blade 157 is disposed, vacuum to port 173 isturned off, pressure to vent 332 is turned on, and the last portion ofthe sheet is transferred to the transfer head. This process is veryquick and takes less than 0.25 seconds. This ensures accurate transferof the sheet even though the platen chain pitch and transfer head pitchmay differ. Alternatively, the vacuum sources could remain on andsufficient pressure could be supplied to overcome the vacuum appliedthereby. During progressive transfer of the sheet, valve 343a remains oncontinuously so that a vacuum is continuously applied to hold theleading edge of the half-cell structure in place on the conveyor. Thevacuum release and pressure blow-off to the zones moves from right toleft along the conveyor of FIGS. 1, 11 and 12, and the sheet ofhalf-cell structure is progressively transferred from right to left ontostacker arm 31. It should be noted that even though the operation of theconveyor and transfer head is described from right to left, it is withinthe scope of the present invention to operate the system of the presentinvention from left to right.

By progressively transferring the cut sheet, the sheet is never allfreely released; it is always engaged with one, the other or both ofconveyor 28 and stacker arm 31. This ensures accurate, repeatableplacement of the sheet on the arm. This accuracy is critical when arm 31places the next top sheet of half-cell structure on the already startedcore 30. Stacker arm 31 is positioned over the core and is lowered toplace the transferred sheet in contact with the core. When thetransferred sheet is placed in contact with the top sheet of the core,the sticky adhesive components lightly stick together, therebypreserving the accuracy of placement. Vacuum source 167 on transfer head31b is relieved, and air pressure from pressure source 168 ismomentarily applied to ports 164, 165 in transfer head bars 162 and 163,thereby releasing the sheet. The stacker arm is then retracted upwardly.

In accordance with the present invention, there is provided an apparatusfor stacking a plurality of sheets of half-cell structure to make ahexagonal-cell honeycomb core. As noted above, the stacking apparatus ofthe present invention is shown at 29 in FIG. 1. The apparatus comprisesmeans for stacking the half-cell structure so that as one sheet of thehalf-cell structure is placed on the top of a stack comprising at leastone sheet of the half-cell structure, the peaks of one sheet contact thepeaks of an adjacent sheet. It should be noted that the half-cellstructure may, in this context, comprise discrete sheets or a continuoussupply. The stacking means comprise stacker arm 31 and stack holder 32.FIGS. 14A, 14B and 15 are cross-sectional views of the stack holder ofthe present invention in greater detail. As shown in FIG. 14A, the stackholder comprises an enclosure surrounding the stacked sheets forrestricting the flow of air around the periphery thereof. An enclosureis shown at 34 in FIG. 14A which comprises an upper portion 185 disposedabove the top of the stack of sheets and a lower portion 187 disposedbelow the top of the stack.

The stacking apparatus of the present invention further includes anelevator 170 as shown in FIG. 14A that comprises a platform 172 having aplurality of guide rods 174 and an elevating screw 178. The stackingapparatus also includes a plurality of end guide plates 176 disposed incontact with the sides of the core. Each guide rod 174 passes through alinear bearing 180, and screw 178 passes through a driven nut 182, whichdrives the screw and attached platform 172, plates 176 and rods 174 upand down. A plurality of auxiliary guide rods 184 are fixed to lowerportion 187 of stack holder enclosure 34. When the sheets of half-cellstructure are placed in the stack holder elevator, they are placed onthe back of platform 172 in contact with guide rods 174 and spaced fromauxiliary guide rods 184.

The stacking apparatus of the present invention also comprisesdifferential pressure means disposed beneath the stack for reducing theair pressure surrounding the stack to a pressure below the air pressureon the top of the stack for pressing the sheets together to form thecore. Preferably, the differential pressure means comprises a blower190a and a circulating blower 190b as shown in FIG. 14A. Blower 190acreates a vacuum on the side on which it communicates with duct 188 anda pressure on the side on which it communicates with duct 189 and duct212 as shown in FIG. 14A. Circulating blower 190b enhances the flow ofair from blower 190a into duct 186. The application of a vacuum to thestack provides a consistent, evenly distributed force to press thesheets of half-cell structure together to form an accurate core.

The purpose of end guide plates 176 is to prevent excess air flow at theends, to register the ends of the assembled core for alignment with thenext sheet of half-cell structure, and to avoid disturbing the ends ofeach sheet as it is lowered onto the core. Preferably, the surfaces ofthe end guide plates are roughened, i.e., roughened enough to oppose thevacuum forces applied to the sheets by vacuum source 190a. The roughenedsurfaces provide a friction force that opposes and balances the vacuumforce on the cut ends of the sheet. One preferred end guide platesurface comprises a rough, cured silicone adhesive which is about 0.08cm. thick. Another surface comprises a plurality of knurled stripsrunning the length of the plate.

The apparatus further comprises first heating means for heating thesheets while the sheets are being stacked. The first heating meanscomprises a heating element disposed in at least one of the upperportion and the lower portion of the enclosure. A heating element 196 isshown in FIG. 14A disposed in lower portion 187. Lower portion 187 alsoincludes a circulating fan 198 which pulls air down past heating element196 and directs the flow against the bottom of enclosure 34. A heatingelement 464 is also disposed in duct 186, which maintains the heat induct 186 and lower portion 187. In the preferred embodiment using theabove-described adhesive system, heating element 464 maintains thetemperature at about 170-190 degrees C. Maintaining this temperaturealso allows the adhesive to continue to cure and the air in the stackholder to remain dry to prevent moisture absorption by the sheet, whichcauses undesirable expansion of some of the materials from which thehalf-cell structure is formed.

In addition, the stacking apparatus of the present invention includessecond heating means for heating air leaking through the enclosure. Thesecond means for heating the air leaking through the enclosurepreferably comprises a duct 189 as shown in FIG. 14A which iscommunication with upper portion 185 of the enclosure. Duct 189 has alow flow of air heated to about 170-190 degrees C in a preferredembodiment and thus limits the inflow of unheated room air that wouldquench the sheet temperature. Duct 189 must include a heating element ifair is drawn into this duct from the atmosphere. Alternatively, air maybe re-circulated from heated duct 186, through duct 188, to duct 189, inwhich case duct 189 does not require a heating element and functionsonly as an air duct. A side panel 191 is provided on upper portion 185to allow access for stacker arm 31 as each sheet is available forstacking. As shown in FIG. 14A, a gate 193 is provided on enclosure 34at the junction of upper and lower portions 185 and 187, respectively,to adjust the amount of air that can freely flow from duct 189 intolower portion 187 and through the core. After each sheet of half-cellstructure is placed on the core, the elevator is lowered by driven nut182 until the top of the just-placed sheet is detected by a plurality ofvertically stacked emitters 192 and receivers 194, which function asupper and lower sensors. The upper emitter and receiver are justuncovered and the lower emitter and receiver remain covered when controlsystem 38 signals the elevator to stop. This is repeated for each sheet.As a result, the core is gradually lowered out of the air stream fromduct 186.

By stacking in a heated enclosure, rapid adhesive curing as each sheetis stacked is ensured. Also, stacking in a heated enclosure keeps thecore dimensionally stable, since sometimes moisture and temperatureeffect sheet dimensions significantly. Applying a vacuum while stackingresults in a pressure differential between the top of the top sheet ofthe core and the rest of the core that presses and holds the just-placedsheet firmly on the core. This differential pressure ensures goodcontact between the peaks of the sheets of half-cell structure, so thefirst and second adhesive components can combine and cure to form astrong, reliable bond. Thus, stacking in a heated enclosure where avacuum is applied achieves an accurate finished core without addededge-aligning dents or holes of the prior art that must be removed fromthe final product after bonding and before the final use thereof. Thecore, as it is assembled, is spongy in the vertical and machinedirections and is rigid only in the transverse machine direction. As theheight of the core increases, the vertical sponginess may increase. Ifthe stacking forces and the half-cell alignment are not controlledcarefully, deformation and mis-registration in the core make stackformation from individual sheets poor or impossible. The reducedpressure caused by the vacuum created in duct 188 provides the requiredstacking force control and also firmly presses the top sheet against thecore to achieve good bonding contact as the adhesive components post-mixand start to set, accelerated by the elevated temperature of the airflow from duct 186.

After the core is fully formed, elevator 170 is raised, and a side door200 provided on upper portion 185 of enclosure 34 is opened to permitremoval of the completed core. Stacking apparatus 29 is then shut downwhile the core is removed. Platform 172, which comprises a foraminousblock, such as a dummy piece of honeycomb, is prepared for the next coreby placing a flat sheet of paper or a thin stainless steel sheet on thetop of the foraminous block. This block allows stable air flow from duct186 to duct 188 at start-up. When the first sheet of half-cell structureis placed on the top of the block by stacker arm 31, it sticks to thesheet placed on top of the block, which ensures that dimensionalaccuracy is maintained for alignment with the next sheet of half-cellstructure.

After removal from the stack holder, the completed core may be placed inan oven for further curing to achieve maximum bond strength. Analternative to shutting down the stacking apparatus for core removal isto provide two stack holders and to alternate stacking between them.Another alternative is to replace the elevator platform with a longheated enclosure with moving endless walls and to provide vacuum andthermal seals around the exiting honeycomb core so it can becontinuously removed and periodically cut off from the already formedcore.

FIG. 15 shows an enlarged cross-sectional view of stack holder 32 ofFIG. 14A in order to more completely explain how the differentialpressure source is applied to press the sheets of the core together.Illustrated in FIG. 15 are a down-flow chamber 202 provided in upperportion 185, a cross-flow chamber 204 provided between ducts 186 and 188and a holding chamber 206 provided below ducts 186 and 188. Cross-flowchamber 204 and holding chamber 206 are part of lower portion 187 ofenclosure 34. The assembled core, which is shown supported on elevatorplatform 172 in FIG. 14A, is positioned with the top sheet of the coreoutside cross-flow chamber 204 in stack holder 32. The pressure, P-lo,in the cross-flow chamber 204, is below the pressure, P-hi, in down-flowchamber 202. Core 30 passes through an opening 214 formed betweendown-flow chamber 202 and cross-flow chamber 204. A plate 195 as shownin FIGS. 14B and 15 is provided in enclosure 34. Plate 195, in additionto adjustable gate 193 and end guide plates 176, restrict fluid flow anddefine opening 214 around the periphery of the top of the core. Airflows from down-flow chamber 202 to cross-flow chamber 204 throughopening 214 all around the periphery of core 30, so the pressure inenclosure 34 changes from P-hi in down-flow chamber 202 to P-lo incross-flow chamber 204 and holding chamber 206. This pressuredifferential from P-hi to P-lo produces a load on the top sheets of thecore, which load is transmitted through the entire core. The forceresulting from the differential pressure is continuously exerted on theremaining core to hold it together during heating and curing in thestack holder.

According to the present invention, there is provided a process ofmaking a hexagonal-cell honeycomb core from a half-cell structure. Theprocess comprises the steps of stacking the half-cell structure so thatas one sheet of half-cell structure is placed on the top of a stackcomprising at least one sheet of half-cell structure, the peaks of onesheet contact the peaks of an adjacent sheet and restricting the flow ofair around the periphery of the stack, such as with enclosure 34. Thestacking step includes stacking the sheets in an enclosure, such asenclosure 34, that restricts the flow of air past the top of the stackinto the enclosure. A differential pressure force may then be applied tothe sheets, such as by blower 190a, during the stacking step to pressthe sheets together, thereby forming the core. The differential pressureforce applied to the sheets may be opposed at the ends of the sheets, asby roughened guide plates 176. The process further includes the step ofpassing a cross-flow of hot gas, such as through ducts 186 and 188,through the stack during the stacking step to rapidly heat the sheets.The process also further includes the step of heating the air passinginto the enclosure surrounding the core, such as through duct 189 andupper portion 185.

In accordance with the present invention, there is provided a process oftransferring a plurality of sheets of half-cell structure. The processcomprises the steps of contacting the valleys on one side of the sheetsof the half-cell structure with a plurality of spaced bars, such as bars162 and 163, formed on a transfer head, such as transfer head 31b, andholding the structure against the bars. Preferably, the bars contact theentire valley of the half-cell structure. A differential pressure force,such as from vacuum source 167, is applied to the sheets through ports,such as 164 and 165, in the bars. Alternatively, the vacuum may beapplied through the spaces between the bars, such as spaces 161. Thepeaks of one side of the half-cell structure are placed in the spacebetween the bars, where the space has a width which is about thedistance between adjacent valleys, and the space is deeper than theheight of the peaks. The sheets may alternatively be adhered to thespaced bars with a temporary adhesive applied to the bars; when thesheet is released from the bars, the valley of the sheet is separatedfrom the adhesive. Alternatively, the sheets may be adhered to thespaced bars with a plurality of clamps and when the sheet is releasedfrom the bars, the valley of the sheet is separated from the clamps. Thetransfer head and the layer are moved from pick-up position 344 in FIG.14A to deposit position 345 as shown in FIG. 14A spaced from the pick-upposition. The sheet is then released from the bars.

An alternate embodiment of the present invention is shown in FIG. 16.Whenever possible in FIG. 16, elements like the elements of theembodiments of FIGS. 1-15 will be used, but will be designated with aprime. In the embodiment of FIG. 16, a differential pressure source isnot used in the stack holder to press the top sheet to the core. Rather,the transfer head is allowed to dwell with the top sheet of the core fora brief time until the adhesive starts to gel before releasing the topsheet. A stacking apparatus is shown in FIG. 16 and includes a stackholder 32' and a stacker arm 31'. Stacker arm 31' includes an extensionrod 31a', a transfer head 31b' and a two-axis shift mechanism 301' whichfunction as described above with respect to FIGS. 10B, 10C and 14A. Thetransfer head of the embodiment of FIG. 16 may include heating means forheating the bars. Preferably, the heating means comprises a heating coil470 as shown in FIG. 16. The heating means may also comprise other typesof heat sources, including, but not limited to, a radiant heater or aresistance heater. Alternatively, heating tape may be wrapped around theperiphery of the bars of the transfer head for heating the bars.

Stack holder 32' also comprises a lower portion 187' of the enclosurefor the stack holder. Disposed in the bottom of lower portion 187' is aheating element 196' and a circulating fan 198' for conditioning the airin the stack holder. An elevator 170' for raising and lowering the coreis provided in lower portion 187', which includes a platform 172' and atleast one guide rod 174' disposed in a linear bearing 180' and at leastone auxiliary guide rod 184'. The elevator functions as described abovewith respect to FIGS. 14A, 14B and 15. An emitter 192' and a receiver194' are provided adjacent core 30' below linear bearing 180' forsensing the position of the core. Preferably, at least one end guideplate 176' is provided for ensuring accurate alignment of the sheets asthey are stacked.

In the embodiment of FIG. 16, transfer head 31b' is allowed to dwellwith the top sheet in contact with the core for a brief time until theadhesive starts to gel before releasing the top sheet. The head dwellensures that the position of the top sheet on the core is retained andwill not shift as the core is lowered on the elevator as the adhesivecontinues to cure. Transfer head 31b' may also travel downwardly withthe elevator before releasing the top sheet on the core. The head ispreferably heated, otherwise it acts as a heat sink for the sheet.Alternatively, when the adhesive system used with the embodiment of FIG.16 does not require heat for curing and maintaining the half-cellstructure in a dry state so that it will not expand, the transfer headof FIG. 16 may be used without heat. Also alternatively, the head couldbe a thermal insulator that would not conduct heat away from the sheet.The adhesive, whether a one-component or a two-component system, ispreferably wet and sticky when the top sheet contacts the core to ensurea large adhesive contact area is quickly formed. However, when thetransfer head of FIG. 16 is used, the need for a sticky adhesive formaintaining an accurate sheet position is decreased.

The operation of the cutting apparatus and the stacking apparatus of thesystem of the present invention as shown in FIGS. 1-15 will now bedescribed with respect to FIG. 17. In normal operation, the half-cellforming apparatus and the adhesive applying apparatus of the presentinvention run continuously and at the same line speed. In describing thetiming diagram of FIG. 17, it will be appreciated that there are manycomponents involved and that there may be several events for eachcomponent, so that many events occur at the same time. This is done tooptimize the cycle time of the system; each could be done sequentially,but more time would be required.

FIG. 17 shows several cycles of operation, starting at an arbitrary zerotime when conveyor 28 begins to advance a sheet-length of the continuoushalf-cell structure. One complete cycle of operation consists of twoconsecutive sheet advances, one where the cut occurs on one side, suchas the upstream side, of a conveyor platen bar, and one where the cutoccurs on the other side, such as the downstream side, of another bar.This requires a lateral shift of one-half the pitch of the half-cellstructure in transfer head 31b to pick up and stack the sheets. Thetypical time for a repeatable cycle of operation is best referenced tothe transfer head shift event and is shown at 216 in FIG. 17. This cycletime is about 3.8 time units on the diagram of FIG. 17.

FIG. 17 will be described looking first at one time unit interval andexamining the components and the events associated therewith generallyfrom top to bottom of the diagram. First, from time 0 to time 1, thefollowing events occur. The conveyor advances the distance of one sheetof half-cell structure and stops. The conveyor then starts to dwell,waiting for the blade to cut a sheet from the continuous supply ofhalf-cell structure and the transfer head to pick up the sheet. Theblade stays in a retracted position, waiting for the conveyor advance tobe completed. Vacuum sources 341a-c of the conveyor of the cuttingapparatus stays on to securely hold the advanced half-cell structurebefore pick-up by transfer head 31b. The conveyor air from pressuresources 336a-c for transferring a cut sheet to transfer head 31b staysoff. The transfer head, which picked up the last sheet at the downstreamcut, stays at that shift position for stacking. Enclosure side panel 191goes from closed to open to admit the transfer head inside enclosure 34for stacking. The transfer head, which is holding the last sheet,continues moving to stack holder 32 and arrives there while conveyor 28is still advancing. Elevator 170 continues moving down until the earlierstacked sheet is at the proper elevation for stacking the next sheet;the elevator dwells at this elevation. When the transfer head is atstack holder 32, and elevator 170 is at the dwell event, the transferhead goes to the down position to place the sheet on top of the stack.When the transfer head is down, vacuum source 167, which had beenholding the sheet securely on the head, is turned off. At the same timethe transfer head air from pressure source 168 is turned on topositively release the sheet from the head, which is still down. Thetransfer head goes to the up position while the transfer head vacuumremains off and the transfer head air remains on. The transfer head,having released the sheet in stack holder 32, starts to move from stackholder 32 to conveyor 28, which may be just before the conveyor reachesthe dwell event. Elevator 170, having received the sheet from thetransfer head, starts moving down.

The following events occur from time 1 to time 2 in FIG. 17. Conveyor 28stays at the dwell event while blade 157 and transfer head 31b interfacewith the half-cell structure on the conveyor. The blade extends acrossthe half-cell structure on the conveyor, thereby cutting through thestructure to cut off a sheet. The blade then retracts back through thecut to return to a retract event position, out of the way of theconveyor bars and the transfer head. The transfer head starts to shiftto an upstream event position while the transfer head is moving to theconveyor, since the sheet to be picked up was just cut at the upstreamside of a conveyor bar. This conveyor bar is one-half of the pitch ofthe half-cell structure away from the position of the bar supporting thesheet adjacent the previous cut. Side panel 191 closes as soon as thetransfer head is clear as it moves to the conveyor. As the transfer headis moving to the conveyor from the stack holder, transfer head pressuresource 168 is turned off, and transfer head vacuum source 167 remainsoff. The transfer head arrives at the conveyor over the cut sheet afterthe blade has retracted. The head has shifted so the transfer head barsare positioned over the spaces on the conveyor platens. Transfer headvacuum source 167 is then turned on. Vacuum sources 343b and 343c arethen turned off, and pressure sources 336a-c are turned on progressivelyfrom one end of the sheet on the conveyor to the other to therebyprogressively transfer the sheet from the conveyor to the transfer headas described in detail above. Transfer head vacuum source 167 stays onto hold the sheet, which has been transferred from the conveyor. Thetransfer head pressure source stays off. The transfer head, afterreceiving the sheet from the conveyor, starts to move to the stackholder. The conveyor then starts to advance.

The above description explains about one half-cycle of operation; a fullcycle is a repeat of this half-cycle, except that the transfer headshift is different. The full cycle keeps repeating until there aresufficient sheets stacked to complete the core, which can be determinedby having distributed control system 38 keep track of how many sheetshave been stacked. When the core is completed, the stacking apparatus isshut off, the enclosure side panel raised, and the stacker elevatorraised so the completed core may be removed from the stack holder.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification beconsidered as exemplary only, with a true scope and spirit of theinvention being indicated by the following claims.

We claim:
 1. An apparatus for stacking a half-cell structure to form ahexagonal-cell honeycomb core, the structure having a plurality of peaksand valleys and a diagonal surface between each consecutive peak andvalley, comprising:(a) means for stacking the sheets so that as onelayer is placed on the top of a stack comprising at least one layer, thepeaks of one layer contact the peaks of an adjacent layer; and (b)differential pressure means disposed beneath the top of the stack forreducing the air pressure surrounding the stack to a pressure below theair pressure on the top of the stack, thereby pressing the sheetstogether to form the core.
 2. The apparatus as claimed in claim 1,wherein the differential pressure means comprises an air blower.
 3. Theapparatus as claimed in claim 1, further including first heating meansfor heating the sheets while the sheets are being stacked.
 4. Theapparatus as claimed in claim 3, wherein the stacking means comprises astack holder and a stacker arm.
 5. The apparatus as claimed in claim 4,wherein the stack holder comprises an enclosure including an upperportion disposed above the top of the stack and a lower portion disposedbelow the top of the stack.
 6. The apparatus as claimed in claim 5,further including second heating means disposed in communication withthe upper portion for heating air leaking through the enclosure.
 7. Theapparatus as claimed in claim 1, further including a plurality of endguide plates disposed in contact with the sides of the core.
 8. Theapparatus as claimed in claim 7, wherein the surfaces of the end guideplates are roughened.
 9. A process of making a hexagonal-cell honeycombcore from a half-cell structure, the half-cell structure having aplurality of peaks and valleys and a diagonal surface between eachconsecutive peak and valley, comprising the steps of:(a) stacking thehalf-cell structure so that as one sheet is placed on the top of a stackcomprising at least one sheet, the peaks of one sheet contact the peaksof an adjacent sheet to form a plurality of hexagonal cells; and (b)applying a differential pressure force to the sheets by reducing the airpressure surrounding the stack to a pressure below the air pressure onthe top of the stack during step (a) to press the sheets together,thereby forming the core.
 10. The process as claimed in claim 9, furtherincluding the step of passing a cross-flow of hot gas through the stackin a direction parallel to the longitudinal axes of the hexagonal cellsduring step (a) to rapidly heat the sheets.
 11. The process as claimedin claim 9, wherein the stacking step includes stacking the sheets in anenclosure, the enclosure restricting the flow of air past the top of thestack into the enclosure and further including the step of heating theair passing into the enclosure surrounding the core.
 12. The process asclaimed in claim 9, further including the step of opposing thedifferential pressure force applied to the sheets at the end of thesheets.